The long term objective of this proposal is to provide knowledge about the identity and function of the protective and regulatory genes that respond to the presence of age-related cataract. The central premise of this proposal is that the lens epithelium is essential for maintaining the normal function of the lens and that functional components of the lens epithelium are responsive to physiological changes induced during cataractogenesis. The Specific Aims of this proposal are: (1) To identify genes of the human lens epithelium whose expression is up- or down-regulated in response to age-related human cataract and to evaluate the potential functions of these genes in the lens. (2) To confirm and to characterize the mRNA levels, protein levels and spatial expression patterns of the identified genes between human lens epithelia dissected from cataractous and normal lenses; To establish the expression levels of the identified genes in specific types of cataracts; and To establish a relationship between the expression levels of these genes and their potential functions in the lens. These aims will be accomplished using integrated approach involving reverse-transcriptase differential display, sequence analysis, cloning of novel differentially expressed genes, semi-quantitative RT-PCR, western analysis, in situ hybridization and immunohistochemistry. The feasibility of this approach is demonstrated by the initial identification of six genes which are up- or down-regulated in response to age-related cataract and the characterization and analysis of three of these genes in normal and cataractous human lenses. One of these genes, called osteonectin or SPARC, was subsequently reported (Gilmour et al., EMBO J., 1998)1 to cause age-onset cataract formation when deleted in mice, further demonstrating the usefulness of the approach outlined in the present study and demonstrating that the genes identified in this proposal may also be candidates for causing cataract when their normal lens function is lost. The information gained from the work proposed here will be used to link cataract-specific gene expression changes with specific lens functions important for the maintenance of lens transparency and should provide a rational basis towards developing methods to retard age-related cataract.